MedicineNet.com

Heart Disease Slideshow Pictures Medical Illustrations of the Heart Image Collection Take the Heart Disease Quiz!

In this Article

• What are implantable cardiac defibrillators (ICDs)?
• How does a normal heart function?
• How do abnormal heart rhythms decrease blood delivery by the heart?
• What is the cause of tachycardias?
• What are the symptoms of tachycardias?
• What are life-threatening tachycardias?
• What are the causes of ventricular tachycardia and ventricular fibrillation?
• How can ventricular tachycardia and fibrillation be treated and prevented?
• Who should receive an ICD?
• How are ICDs designed?
• How are ICDs implanted?
• What happens after implantation of an ICD?
• What are the complications of ICD implantation?
• What happens during a tachycardia episode after the placement of an ICD?
• Living with an ICD.
• What outside electrical sources are safe?
• What outside electrical sources can interfere with the ICD?
• What does the future hold for ICDs?
• Implantable Cardiac Defibrillators At A Glance
• Implantable Cardiac Defibrillator Index
• Find a local Cardiologist in your town

What is the cause of tachycardias?

Abnormally fast heart rates are called tachycardias. Tachycardias are caused by rapidly firing electrical signals arising from the walls of the atria or the ventricles. These rapidly firing signals override the signals generated by the SA node and cause the heart to beat too fast.

Tachycardias caused by electrical signals from the atria are called atrial tachycardias. Tachycardias caused by electrical signals from the ventricles are called ventricular tachycardias.

What are the symptoms of tachycardias?

Symptoms of tachycardias include:

1. Palpitations or fluttering sensations in the heart;
2. Lightheadedness (due to low blood pressure);
3. Fainting spells or loss of consciousness (due to low blood pressure);
4. Fatigue and weakness (due to lack of blood supply); and
5. A flushing sensation.

Please see the Palpitations article of MedicineNet.com for information on the symptoms, causes, and diagnosis of tachycardias.

What are life-threatening tachycardias?

Two common life-threatening tachycardias are ventricular tachycardia and ventricular fibrillation. Ventricular tachycardia is a rapid regular rhythm caused by electrical signals originating from an area of the ventricle. Ventricular tachycardia can decrease blood delivery by the heart and cause low blood pressure. Ventricular tachycardia can also progress to a more serious heart rhythm called ventricular fibrillation.

Ventricular fibrillation is an irregular rhythm, which is a result of multiple rapid and chaotic electrical signals firing from many different areas in the ventricles. A heart undergoing ventricular fibrillation is in a state of standstill called cardiac arrest. The heart muscles quiver and cease pumping which causes a halt in the delivery of blood to the body. Unless ventricular fibrillation is terminated quickly, irreversible brain damage occurs within minutes of the onset of ventricular fibrillation, leading to death.

Sudden cardiac arrest is the most common cause of death in the United States. About 450,000 Americans suffer cardiac arrest each year. 80 to 90% of these patients die before reaching the hospital. The most frequent causes of cardiac arrest in the United States are ventricular tachycardia and ventricular fibrillation.